Furnace not getting warm enough - 2020 Momentum 397TH

[amullineaux]

We recently purchased a 2020 Momentum 397TH in march. We really like it, except we have one major concern. The furnace will not get the temperature warm enough. We mainly dry camp and sometimes the outside temps are low. We just spent the last 3 days where the outside temps got down to 30 degrees at night. We set the furnace to 60 degrees and the furnace runs non-stop all night, but never gets up to 60 degrees in both the main living area and the bedroom. 54 degrees was as warm as it got. Once the sun came up, it warmed right up to 60 degrees and the furnace shut off. This surely isn't right. We traded our 2017 Fuzion in on this, and it had no problem staying warm in the cooler temperatures, so I know the momentum should do the same. We also notice that while the air is warm coming out of the vents, it is not coming out with very much force. There are only 2 vents in the main living area under the island, one in the bathroom and one in the bedroom. Nothing in the garage ?? Does anyone have any ideas on why this does not get warm enough ? I will be contacting a service center. Thank you !

[TucsonJim]

Hi, and welcome to the forum.

Do you have any kind of thermometer that you can use to measure the temperature coming out of each vent? And when it's running, dangle a piece of paper over each vent to make sure there is good airflow. My suspicion is that one of the ducts has come loose.

Also, what do you have the fan setting on? Lo, hi, or auto?

Jim

[amullineaux]

We have the touch screen control, so I don't really see a hi/med/low fan setting. I don't feel like there is enough airflow coming out of the ducts. It is warm, but it is not coming out with much force. My thought has been there is a "kink" in the ducts, or one possibly came loose, except all the ducts seem to have the same weak airflow coming out of them.

[TucsonJim]

If you have the Lippert One Control in your unit, the fan speed should be adjustable. Check out this video to see if it's the same as yours. When you open the link, click on the "Generator and HVAC" tab for the correct video.

https://www.lci1.com/onecontrol#OC-videos

If that doesn't solve it, then I'd have to agree that you might have a kinked or loose duct somewhere in the system. If you want to try and trace the problem yourself, I can check out your floor plan HVAC drawings to try and determine how the ducts are routed.

Jim

[amullineaux]

I will check out the video, and yes.... I would greatly appreciate a floorplan drawing of the heater vents. Thank you very much !

[colan]

The fan speed control is for the AC fan. The furnace only has one fan speed.

[Cate&Rob]

. . . except all the ducts seem to have the same weak airflow coming out of them.

This would point to the problem being right at the furnace. Usually the furnace output goes into a box (on the furnace) with various ducts going off to different locations. If a major duct connection has come apart at the furnace, there will not be enough airflow to any of the other ones. If the problem were an internal air flow blockage within the furnace, the high temp limit switch would likely be shutting things down and this is not happening. I would suggest that you get eyes on the the furnace installation first. Usually not too difficult to see behind the easily removable aft wall in the pass through storage area.

Rob

[JBill9694]

We recently purchased a 2020 Momentum 397TH in march. . . . one in the bathroom and one in the bedroom. Nothing in the garage ?? !

If it is just the full bathroom that has the heat you probably want to be sure to leave the half-bath door open to help get heat into this area so that the waterlines don't freeze.

In the garage, take a close look along the front wall, especially at the base of the connecting door. We have a row of 14 round holes below our door threshold and it took some careful observation to figure out that these are the heat vent for the garage, but it's probably not enough. There are several threads on this site that talk about supplementing the garage heat with a small electrical heater.

[amullineaux]

Thank you for the replies. Yes.. the fan speed is only for the AC. I will try to look at the furnace itself to see if there is an issue in the ducts at the source. How do I access the furnace to look at the ducts ? I see the exhaust panel on the outside by the water heater. I will also look in the garage under the connecting door to see if I have little holes. Either way... it is definitely not enough heat back there. I also have a call in to grand design service to see what they say. In the mean time.... if anyone knows how I access the furnace, I will check that. I will keep you posted.

[Cate&Rob]

if anyone knows how I access the furnace, I will check that.

From looking at your floorpan, the furnace should be below the water heater on the street (left) side just aft of the water connection panel. You can confirm this by where the outside furnace cover is. To access this area, there are normally a few screws retaining the aft wall panel in the pass through storage area. (Behind the water connection and valves panel). Removing this wall should give you access to the furnace.

Caveat: I don't have a Momentum, so perhaps someone who does could chime in on whether my guess about how to get to the furnace is correct.

Rob

[d2reid]

I have a 2017 Momentum 376 so while it's a Momentum things could be different. But on mine Rob is correct, the heater is behind the wall. There is a lot of other stuff behind that wall also so getting hands on the heating unit is going to be a contortionist act. Just be careful not to pull the wire loose, that area is not engineered.

In testing I like a 1/2 inch strip of toilet paper about 6" long, it flutters pretty good. Then the cheap thermometer in the vent to see what the temps coming out really are.

Another common problem has been a hose connection cover plate coming off, letting all the air blow into the area behind the cabinet. Cover plate laying next to the heater with the set screwing being someplace close on the floor. Before you get started pick up a roll of aluminum HVAC sealer tape. Great for covering those little mistakes, also works good when the A/C buffer falls down, another story.

While your back there looked for crushed ducks. Sorry, crushed ducts. And of course loosely connected ducts. All have been witnessed.

And the last thing to check is your expectations. These heaters are not very strong. The air flow is not overwhelming at all. We winter in ours at ski resorts so have run it in very cold conditions. We can typically get the cabin temperature up to 65, but without additional heat that's about as good as it gets. So it may be time well spent looking at where heat might be lost as well. My two favorite mistakes are to leave the over head fan open or leave a bay door open. My wife likes to open the window by the bathroom and then pull the shade down. Loose fitting door seals and slides not fully sealing have been issues as well. Just stuff to check...

[Country Campers]

Man I hope you do not find any "crushed ducks" under there that would be bad..

Sorry Dallas I could not resist.

Brian

[JBill9694]

Another way to get a view of the ducts may be to pull the cover from what for lack of a better term I'll call the air return. In our Momentum this is at the bottom of the pantry and is partially hid behind the pantry door. The air return is not ducted to the furnace, just provides for air flow back into the mechanical area, so it can be used to get a look at the furnace and ducts from another direction.

If you pull one of the basement bulkheads to access the furnace it would be a good chance to get familiar with the location of other things like the water heater, water pump, inverter, etc., and to check for any water leaks.

[amullineaux]

Thank you all so much for taking the time to try and help me. I know this unit should be able to at least heat up into the low 60's with really cold outside temps. My Fuzion that I traded in was used during hunting season many times when the outside temps got down to the single digits. Granted... the heater ran a lot.... but it stayed 65 degrees in there. The momentum is only slightly bigger than the fuzion, so I am surprised at the lack of heat. I did get a small heater to put in the garage area if needed to keep that area warm. I am taking it in to a service facility next week. Wish me luck !

[colan]

We also have a 397TH, airflow through the heating ducts is nothing to write home about. Furnace is fine, all the ducts are attached. My thoughts are it is the nature of the beast. Too many runs, too many feet of ductwork, too many turns...